Adhesive of folded package

ABSTRACT

A package includes a flexible substrate with a first region and a second region, an encapsulated die supported by the first region, and a conformable fold adhesive introduced between the encapsulated die and the flexible substrate. The second region of the flexible substrate is folded over the surface of the encapsulated die.

BACKGROUND

For semiconducting devices, increase in speed, in functionality and thusperformance, is often associated with increased size for thesemiconducting device packages. However, it is desirable to reduce theoverall height of the package, to allow for greater integration andflexibility.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view illustrating one embodiment of a package prior tofolding.

FIG. 2 is a side view illustrating one embodiment of the package of FIG.1 after folding.

FIG. 3 is a side view illustrating one embodiment of the package of FIG.2 with a top package stacked thereover.

FIG. 4 is a flow chart illustrating steps of one embodiment to form apackage.

FIG. 5 is a side view illustrating one embodiment of a package with dualdie encapsulants.

FIG. 6 is a side view illustrating another embodiment of a package withdual die encapsulants.

FIG. 7 is a depiction of a system according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description reference is made to theaccompanying drawings. In the drawings, like numerals describesubstantially similar components throughout the several views. Otherembodiments may be utilized, and structural, logical, and electricalchanges may be made.

FIG. 1 illustrates one embodiment of a package 10. The package 10includes a flexible substrate 12 with a first region 13A, a secondregion (or flap) 13B, a front side 14, and a back side 16. The package10 includes wire bonds 17 that electrically couple a die 24 with thesubstrate 12. The substrate 12 supports the die 24 on the front side 14at the first region 13A. A die encapsulant 25 encapsulates the die 24and the wire bonds 17. In one embodiment, not shown, the die 24 issupported by a die attach layer on the substrate.

The package 10 also includes solder balls 15 formed on the back side 16at the first region 13A. The solder balls 15 in a ball grid array aremounted to form an electrical-mechanical connection between die 24 andother electrical devices. At the back side 16 of the substrate 12 at thesecond region 13B are land pads 16A or bond pads at which various memorydevices (such as top package 40 in FIG. 3) can be attached, as describedin more detail below.

The thickness of flexible substrate 12 is typically about 0.1 mm. In oneembodiment, the flexible substrate 12 is a polyimide tape basedmaterial. Conductive paths for electrical communication are formed inflexible substrate 12. In one embodiment, the flexible substrate hasconductive traces, such as copper wires, along the length of one or bothsurfaces/sides of the substrate 12 for electrical connections. In oneembodiment, the electrical traces wrap around the edges of the substrateor electrically connect through the substrate. A number of materials maybe used for the flexible substrate 12 and the conductive paths therein.The choice of materials will depend on the relevant circuit designconsiderations and the costs that are associated with fabricating thepackage 10 (among other factors).

The die encapsulant 25 typically has a thickness in a range from about0.2 mm to about 0.5 mm. The die encapsulant is epoxy or some othersuitable material, in this embodiment. A number of materials may be usedfor the die encapsulant. The choice of materials will depend on therelevant circuit design considerations and the costs that are associatedwith fabricating the semiconducting package.

In this embodiment, the package 10 includes a fold adhesive 26 that ismanually or automatically dispensed over a surface 25A of the dieencapsulant 25. In one embodiment, a predetermined amount of adhesive 26is dispensed. In this embodiment, the adhesive 26 is compliant and ableto deform under stress, as discussed in more detail below.

In other embodiments, other fabrication processes such as lead bonding,bump bonding, and die stacking are typically performed on die 24 priorto die encapsulation. It should be noted that packages may include anynumber of units of die and die encapsulant, and they can be formed onthe front side 14 or back side 16 of the flexible substrate 12 at thefirst region 13A or at the second region 13B.

As shown in FIG. 2, the packaging process includes folding the flexiblesubstrate 12 over the die encapsulant 25 such that the land pads 16A areon top of the package 10. The second region 13B of the front side 14 ofthe flexible substrate contacts the fold adhesive 26, as does thesurface 25A of the die encapsulant 25. The fold adhesive 26 is thencured to hold the folded package 10 together. In one embodiment, curingthe fold adhesive includes a partial cure of the fold adhesive using atemperature and/or pressure cure process, and then a substantially fullcure using a temperature batch cure process, as described in more detailbelow.

In a first embodiment, the fold adhesive is a conformable fold adhesive.In this embodiment, the conformable folding adhesive is able to conformto a warped surface to form a substantially flat surface. In oneembodiment, the conformable fold adhesive has a volumetric cureshrinkage of less than about 0.8%. In an additional embodiment, theconformable fold adhesive has a Young's modulus of less than about 600MPa at about room temperature. In yet another additional embodiment, theconformable fold adhesive has an elongation at break greater than about100% at about room temperature. In one embodiment, the fold adhesive hasa low Young's modulus and a high elongation prior to break. Theconformable fold adhesive, in one embodiment, has one of thesecharacteristics, but may have two or more of the variouscharacteristics. In one embodiment, the fold adhesive is a film. Inanother embodiment, the fold adhesive 26 is a paste.

In one embodiment, the fold adhesive 26 is dispensed directly onto thesurface 25A of the die encapsulant 25. In an additional embodiment, thefold adhesive 26 is dispensed directly onto the front side 14 at thesecond region 13B of the substrate 12, and then the substrate 12 isfolded over where the adhesive 26 aligns with the die encapsulant 25.

In one embodiment, the fold adhesive is made of at least one ofsilicone, a silicone based polymer, a silicone modified epoxy, and apolyimide-siloxane based system. In one embodiment, the fold adhesive ismade of at least one of vinyl terminated silane, hydrogen terminatedsilane, platinum catalyst, fumed silica and other filler particles. Inone embodiment, the fold adhesive is made of at least one of polyimidesiloxane, aliphatic epoxy, phenol hardener, and imidazole catalyst. Inone embodiment, the fold adhesive is made of at least one of an epoxy,an amine end capped silicone, phosphine catalyst, and a silica filler.The following tables list examples of percentage by weight for eachcomponent in embodiments of a fold adhesive.

EXAMPLE 1

Component Weight % Vinyl terminated silane 50–80 Hydrogen terminatedsilane 10–30 Platinum catalyst Less than 1 Fumed silica  5–10

EXAMPLE 2

Component Weight % Polyimide siloxane 60–90 Aliphatic epoxy  5–10 Phenolhardener  5–10 Imidazole catalyst Less than 1

EXAMPLE 3

Component Weight % Epoxy 40–80 Amine end capped silicones 20–40Phosphine catalyst Less than 1 Silica filler 10–40

FIG. 3 illustrates an embodiment with a bottom folded stack package 30,and a top package 40 supported by the bottom folded stack package 30.The bottom package 30 is similar to the package 10. After folding theflap of the flexible substrate over the die encapsulant 25, the backside 16 of the flap 13B of the flexible substrate 12 becomes asubstantially flat upper surface 27 of the package 10.

The substantially flat upper surface 27, as shown in FIG. 2, has bondpads 16A that are used to secure the bottom package 30 to the toppackage 40. Bumps of the top package 40 are aligned to the bonding pads16A on the bottom package 30 and the packages are brought together, suchthat the top and bottom packages are stacked one on top of another. Inone embodiment, the solder bumps on the top package are soldered to thebonding pads on the bottom package to form contacts 35. In oneembodiment, the contacts 35 secure and electrically couple the top andbottom packages.

In one embodiment, reliability of the contacts 35 (or solder joints)between the top package 40 and the bottom package 30 is maximized. Inone embodiment, shear stress exists on the contacts 35 (or solderjoints) during temperature cycling of the package or device. This shearstress is partially a result of a difference in the coefficients ofthermal expansion (“CTE”) between the top and bottom packages. In thisembodiment, this shear stress decreases the reliability of the contacts35. In an embodiment, solder joint stress is substantially transferredto the compliant fold adhesive 26. In one embodiment, the fold adhesive26 has compliant characteristics of a relatively high elongation (anelongation at break greater than about 100% at about room temperature),and a relatively low Young's modulus (less than about 600 MPa at aboutroom temperature). Accordingly, because of the substantial transfer, thesolder joints have a minimized strain level and are substantiallyprevented from deforming under stress.

With a substantially flat upper surface 27, a z-height of the bottompackage is minimized in one embodiment. The bottom folded packagewarpage substantially determines the overall stacked package warpage andthe z-height of the bottom package. In one embodiment, the bottompackage warpage is substantially governed by the unfolded packagewarpage (including shrinkage of the die encapsulant) and the warpagethat may be further induced by folding adhesive cure shrinkage. By usingthe low cure shrinkage, high elongation, folding adhesive 26, theoverall bottom package warpage and z-height is minimized in oneembodiment. In this embodiment, the folding adhesive 26 conforms to thesurface 25A of the warped die encapsulant to form a substantially flatsurface of the folding adhesive. In an additional embodiment, theadhesive 26 does not cause further warpage to the bottom package due tothe minimal cure shrinkage, more particularly, a volumetric cureshrinkage of less than about 0.8%. With the minimized z-height of thebottom package, a successful bottom package to top package stackingprocess is likely.

The plurality of contacts 35 provides additional conductive paths fordelivering signals and power between and/or to the top package 40 andthe bottom package 30. The plurality of contacts 35 may also decreasethe overall distance of many of the conductive paths within the package10 depending on the design of the package 10. Although in the exampleembodiment illustrated, each of the contacts 35 are a solder column or areflowed solder bump, it should be noted that any type of contact 35 maybe used as long as contact 35 extends from the flexible substrate to thetop package. For example, in an additional embodiment, the bottom andtop packages are electrically and mechanically coupled using anadhesive, bumps (including solders or plastics), a conductive epoxy orsome form of solder attachment, among other methods.

In this embodiment, the top package 40 includes a first die 42, a seconddie 44 supporting the first die 42, a spacer 46 between the first andsecond dice 42, 44, and wire bonds 48. The wire bonds 48 electricallycouple the first and second dice 42, 44 with a substrate 50 upon whichthe dice 42, 44, are dispensed. The dice 42, 44, the spacer 46 and wirebonds 48 are encapsulated by a die encapsulant 52 similar to the dieencapsulant described above. Other embodiments for the top package 40are possible and depend upon the relevant circuit design considerations.In one embodiment, the spacer 46 is an epoxy or polyimide material,similar to a die attach layer, discussed in more detail below. Inanother embodiment, not shown, a die attach layer is dispensed betweenthe second die 44 and the substrate 50.

In the embodiment of FIG. 4, the die encapsulant 25 encapsulates the die24 at the first region 13A of the substrate 12. At 100, a plasma cleanis performed to remove any releasing agents on the surface 25A of thedie encapsulant 25 and on a front side 14 of the second region 13B ofthe substrate 12 before dispensing the fold adhesive. The releasingagents may have been left by the molding process.

In one embodiment, the plasma clean is performed by flowing oxygen intoa reaction chamber having a plasma generating rf source powered at 50 to250 watts. This low power is used to minimize chemical reactions. Theflow of oxygen plasma contacts the releasing agents, removing thereleasing agents particles from the surface and charging the particles.The charged particles are then purged from the chamber by the gas flowand vacuum. Though the use of oxygen gas is described in the plasmaclean step, one with skill in the art would realize that any heavymolecular gas could be used. Other gasses which could be used includeargon and nitrogen. In an additional embodiment, the plasma clean isperformed using a reactive ion etching. The reactive ion etching uses areactive gas such as CF₄ or SF₆ or O₂, or mixtures thereof, and thisreactive gas chemically attacks the surface to remove the releasingagents.

At 110, the fold adhesive 26 is dispensed over the die encapsulant 25.At 120, the flap 13B of the flexible substrate 12 is folded over thefold adhesive 26 and the die encapsulant 25. At 130, temperature and/orpressure is applied for a very short time period to partially cure thefold adhesive. In one embodiment, at step 130, the temperature isbetween about 150° C. and 200° C., and the pressure is applied for lessthan about 30 seconds. At 140, a batch cure process at about 150° C.using a Blue M® (General Signal Technology Corporation) oven completesthe fold and adhere process in one embodiment. In this embodiment, theoven has temperature profile capability, such as the ability to controlthe temperature in the oven, the length of time at that temperature, aswell as the rate of temperature increase/decrease.

Although the adhesive was described in FIGS. 1 to 3 in the context of abottom package with a single encapsulated die, other embodiments arepossible and depend upon the relevant circuit design considerations.Further, although the embodiment of FIG. 3 was described as having thebottom package 30 and the top package 40, the packages may be invertedsuch that the package 30 is “on top of” the package 40. In an additionalembodiment, there may be two packages 30, one on top of another, or twopackages 40, one on top of another.

Also, consider for example, FIGS. 5 and 6. In the embodiments of FIGS. 5and 6, packages 60 and 70 are illustrated. In embodiments, the packages60 and 70 may be bottom and/or top packages.

In the embodiment of FIG. 5, the package 60 includes the flexiblesubstrate 12 supporting a first single die encapsulant 61 at the secondregion 13B and a second single die encapsulant 62 at the first region13A. The first and second single die encapsulants 61 and 62 are similarin this embodiment. Top surfaces of the first and second single dieencapsulants 61 and 62 are joined upon folding the substrate 12, similarto previous embodiments. The adhesive 26 is dispensed between the dieencapsulants 61 and 62, onto either encapsulant. The die encapsulant 62encapsulates a die 64 supported on a die attach layer 66, and wire bonds68 electrically coupling the die with the substrate 12. The dieencapsulant 61 has similar elements and characteristics to the dieencapsulant 62, in this embodiment. In one embodiment, the die attachlayer 66 is made of a material that includes at least one of an epoxy ora polyimide. The die attach layer 66 may have a thickness ⅓ to ½ that ofthe die.

In one embodiment of FIG. 6, the package 70 includes the flexiblesubstrate 12 supporting a first multiple die encapsulant 72 and a secondmultiple die encapsulant 74. The first and second single multipleencapsulants 72 and 74 are similar in this embodiment. Top surfaces ofthe first and second multiple die encapsulants 72 and 74 are joined uponfolding the substrate 12, similar to previous embodiments. The adhesive26 is dispensed between the die encapsulants 72 and 74, onto eitherencapsulant. The die encapsulant 72 encapsulates a first die 76supported on a die attach layer 78, a second die 80 supported by aspacer 82 between the first die 76 and the second die 80, and wire bonds84 electrically coupling the dice 76, 80 with the substrate 12. The dieencapsulant 72 has similar elements and characteristics to the dieencapsulant 74, in this embodiment.

FIGS. 1 to 6 are merely representational and are not drawn to scale.Certain proportions thereof may be exaggerated, while others may beminimized. Many other embodiments will be apparent to those of skill inthe art upon reviewing the above description. Parts of some embodimentsmay be included in, or substituted for, those of other embodiments.

Although the inventive concept may be discussed in the exemplary contextof a folded stack bottom package, the claims are not so limited. Indeed,embodiments of the present invention may well be implemented as part ofany package system, including an electronic system such as a wirelesssystem or a computer system. The elements, materials, geometries,dimensions, and sequence of operations can all be varied to suitparticular packaging requirements.

FIG. 7 is a depiction of a system 700 according to an embodiment. In oneembodiment, the system 700 is a wireless system. In other embodiments,the system 700 is a computer system. In still other embodiments, thesystem 700 is any type of electronic system. Some examples of system 700include but are not limited to cellular telephones and other wirelessdevices or communicators, computers, personal digital assistants (PDAs)or other hand-held devices, workstations, radios, video players,vehicles (e.g. an automobile, a locomotive, an aircraft, a watercraft,and a spacecraft), and the like.

The system 700 comprises at least one package 710, an input device 720and an output device 730. In one embodiment, the package 710 includes afold adhesive described in at least one of the embodiments herein. Thepackage 710 may include any semiconducting device, for example, amicroprocessor, a microcontroller, memory, a graphics processor or adigital signal processor, and/or a custom circuit or anapplication-specific integrated circuit, such as a communicationscircuit for use in wireless devices such as cellular telephones, pagers,portable computers, two-way radios, and similar electronic systems. Inone embodiment, an input device 720 and an output device 730 are eachcommunicatively coupled to the package 710. The input device 720 is anytype of device to receive data from a user or another system. Someexamples of input devices include a mouse, a trackball, a touchpad, akeyboard or a voice-controlled device or a microphone. The output deviceis any type of device to output data to a user or another system. Someexample output devices include a display device or a speaker.

In some embodiments, the system may further include a voltage sourcethat is electrically coupled to the semiconducting device. Voltagesource may be used to supply power to a die (e.g., a processor) that iswithin semiconducting device.

The system may also include an external memory that in turn includes oneor more memory elements suitable to the particular application, such asa main memory in the form of random access memory (RAM), one or morehard drives, and/or one or more drives that handle removable media, suchas floppy diskettes, compact disks (CDs) and digital video disks (DVDs).

The Abstract is provided to comply with 37 C.F.R. §1.72(b) requiring anAbstract that will allow the reader to quickly ascertain the nature andgist of the technical disclosure. It is submitted with the understandingthat it will not be used to interpret or limit the scope or meaning ofthe claims.

In the foregoing Detailed Description, various features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the inventionrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the Detailed Description, with eachclaim standing on its own as a separate preferred embodiment.

It will be readily understood to those skilled in the art that variousother changes in the details, material, and arrangements of the partsand method stages which have been described and illustrated in order toexplain the nature of this invention may be made without departing fromthe principles and scope of the invention as expressed in the subjoinedclaims.

1. A method of forming a package comprising: supporting a die on aflexible substrate; encapsulating the die with a die encapsulant;folding a flap of the flexible substrate over the die encapsulant;introducing fold adhesive between the folded flap of the flexiblesubstrate and a surface of the die encapsulant; conforming the foldadhesive to the surface such that the fold adhesive is substantiallyflat; and curing the fold adhesive, wherein the fold adhesive has avolumetric cure shrinkage of less than about 0.8%.
 2. The method ofclaim 1 wherein curing includes a partial cure of the fold adhesiveusing a cure process with at least one of temperature and pressure, andthen a substantially full cure using a temperature batch cure process.3. The method of claim 1 further comprising plasma cleaning to removereleasing agents on the surface of the die encapsulant and on a frontside of the substrate before dispensing the fold adhesive.
 4. The methodof claim 1 wherein the fold adhesive is dispensed onto the dieencapsulant before the flexible substrate is folded over the dieencapsulant.
 5. The method of claim 1 wherein the volumetric cureshrinkage of the adhesive facilitates a back side of the flexiblesubstrate at the folded flap to become a substantially flat uppersurface of the package.
 6. The method of claim 5 further comprisingminimizing a z-height of the flexible substrate.
 7. The method of claim1 further comprising supporting a top package upon the folded flap ofthe flexible substrate.
 8. A method of forming a package comprising:supporting a die on a flexible substrate; encapsulating the die with adie encapsulant; folding a flap of the flexible substrate over the dieencapsulant; introducing fold adhesive between the folded flap of theflexible substrate and a surface of the die encapsulant; conforming thefold adhesive to the surface such that the fold adhesive issubstantially flat; supporting a top package upon the folded flap of theflexible substrate; and providing solder joints between the top packageand a substantially flat upper surface of the folded flap of theflexible substrate; and maximizing reliability of the solder joints bytransferring a substantial amount of stress from the solder joints tothe fold adhesive, wherein the fold adhesive is substantially compliantdue to a Young's modulus of less than about 600 MPa at about roomtemperature, and an elongation at break greater than about 100% at aboutroom temperature.
 9. The method of claim 1 wherein the fold adhesive isselected from the group consisting of at least one of silicone, asilicone modified epoxy, a polyimide-siloxane based system, vinylterminated silane, hydrogen terminated silane, platinum catalyst, fumedsilica, polyimide siloxane, aliphatic epoxy, phenol hardener, imidazolecatalyst, an epoxy, an amine end capped silicone, phosphine catalyst, asilica filler and other filler particles.
 10. The method of claim 1wherein the fold adhesive is selected from the group consisting of atleast one of silicone, a silicone modified epoxy, and apolyimide-siloxane based system.
 11. A method of forming a packagecomprising: supporting a die on a flexible substrate; encapsulating thedie with a die encapsulant; folding a flap of the flexible substrateover the die encapsulant; introducing fold adhesive between the foldedflap of the flexible substrate and a surface of the die encapsulant; andconforming the fold adhesive to the surface such that the fold adhesiveis substantially flat, wherein the fold adhesive is selected from thegroup consisting of at least one of vinyl terminated silane, hydrogenterminated silane, platinum catalyst, fumed silica and other fillerparticles.
 12. The method of claim 1 wherein the fold adhesive isselected from the group consisting of at least one of polyimidesiloxane, aliphatic epoxy, phenol hardener, and imidazole catalyst. 13.The method of claim 1 wherein the fold adhesive is selected from thegroup consisting of at least one of an epoxy, an amine end cappedsilicone, phosphine catalyst, and a silica filler.
 14. The method ofclaim 8 wherein the volumetric cure shrinkage of the adhesivefacilitates a back side of the flexible substrate at the folded flap tobecome a substantially flat upper surface of the package.
 15. The methodof claim 8 further comprising minimizing a z-height of the flexiblesubstrate.
 16. The method of claim 11 further comprising curing the foldadhesive, wherein the fold adhesive has a volumetric cure shrinkage ofless than about 0.8%.
 17. The method of claim 11 further comprisingpartial curing of the fold adhesive using a cure process with at leastone of temperature and pressure, and then a substantially full cureusing a temperature batch cure process.